[PL] Rename getTuple into call operator.

This simlifies access to the values while maintaining simple interface.

ProcessLib/Parameter/ConstantParameter.h

@@ -31,7 +31,7 @@ struct ConstantParameter final : public Parameter<T>
         return static_cast<unsigned>(_value.size());
     }
 
-    std::vector<T> const& getTuple(
+    std::vector<T> const& operator()(
         double const /*t*/, SpatialPosition const& /*pos*/) const override
     {
         return _value;

ProcessLib/Parameter/MeshElementParameter.h

@@ -34,8 +34,8 @@ struct MeshElementParameter final : public Parameter<T> {
         return _property.getNumberOfComponents();
     }
 
-    std::vector<T> const& getTuple(double const /*t*/,
-                                   SpatialPosition const& pos) const override
+    std::vector<T> const& operator()(double const /*t*/,
+                                     SpatialPosition const& pos) const override
     {
         auto const e = pos.getElementID();
         assert(e);

ProcessLib/Parameter/MeshNodeParameter.h

@@ -34,8 +34,8 @@ struct MeshNodeParameter final : public Parameter<T> {
         return _property.getNumberOfComponents();
     }
 
-    std::vector<T> const& getTuple(double const /*t*/,
-                                   SpatialPosition const& pos) const override
+    std::vector<T> const& operator()(double const /*t*/,
+                                     SpatialPosition const& pos) const override
     {
         auto const n = pos.getNodeID();
         assert(n);

ProcessLib/Parameter/Parameter.h

@@ -52,7 +52,7 @@ struct Parameter : public ParameterBase
     virtual unsigned getNumberOfComponents() const = 0;
 
     //! Returns the parameter value at the given time and position.
-    virtual std::vector<T> const& getTuple(
+    virtual std::vector<T> const& operator()(
         double const t, SpatialPosition const& pos) const = 0;
 };